U.S. patent number 11,289,891 [Application Number 16/522,998] was granted by the patent office on 2022-03-29 for method and device for reducing leakage currents.
This patent grant is currently assigned to Dr. Ing. h.c. F. Porsche Aktiengesellschaft. The grantee listed for this patent is Dr. Ing. h.c. F. Porsche Aktiengesellschaft. Invention is credited to Tim Pfizenmaier, Daniel Spesser.
United States Patent |
11,289,891 |
Spesser , et al. |
March 29, 2022 |
Method and device for reducing leakage currents
Abstract
A method for reducing leakage currents in a protective conductor
of an electricity network including a neutral conductor and a phase
conductor in addition to the protective conductor. A differential
current is determined depending on a phase conductor current in the
phase conductor and a neutral conductor current in the neutral
conductor. A compensation current is fed into the phase conductor
and/or into the neutral conductor. The compensation current
compensates for a leakage current caused by the differential
current. Also described is a device for carrying out such a
method.
Inventors: |
Spesser; Daniel (Illingen,
DE), Pfizenmaier; Tim (Leonberg, DE) |
Applicant: |
Name |
City |
State |
Country |
Type |
Dr. Ing. h.c. F. Porsche Aktiengesellschaft |
Stuttgart |
N/A |
DE |
|
|
Assignee: |
Dr. Ing. h.c. F. Porsche
Aktiengesellschaft (N/A)
|
Family
ID: |
65818147 |
Appl.
No.: |
16/522,998 |
Filed: |
July 26, 2019 |
Prior Publication Data
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|
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Document
Identifier |
Publication Date |
|
US 20200036180 A1 |
Jan 30, 2020 |
|
Foreign Application Priority Data
|
|
|
|
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Jul 27, 2018 [DE] |
|
|
102018118259.7 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H02H
9/08 (20130101); H02H 1/04 (20130101); B60L
53/30 (20190201); H02H 3/46 (20130101); H02J
7/02 (20130101); G01R 31/52 (20200101); Y02T
10/70 (20130101); Y02T 10/7072 (20130101); Y02T
90/12 (20130101) |
Current International
Class: |
H02H
1/04 (20060101); H02H 3/46 (20060101); H02J
7/02 (20160101); B60L 53/30 (20190101); G01R
31/52 (20200101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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10139028 |
|
May 2002 |
|
DE |
|
102008024348 |
|
Dec 2009 |
|
DE |
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2372857 |
|
Oct 2011 |
|
EP |
|
3013848 |
|
May 2015 |
|
FR |
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2017001950 |
|
Jan 2017 |
|
WO |
|
Other References
A Albanna, M. N. Arafat, A. Gupta, M. Anwar and M. Teimor,
"Analysis of ground fault currents in isolated and non-isolated
charging modules in electric vehicles," 2015 IEEE Transportation
Electrification Conference and Expo (ITEC), 2015, pp. 1-6 (Year:
2015). cited by examiner .
Chinese Office Action for Chinese Application No. 201910655390.9,
dated May 6, 2021, 9 pages. cited by applicant .
European search report dated Oct. 18, 2019. cited by
applicant.
|
Primary Examiner: Miller; Daniel R
Attorney, Agent or Firm: RatnerPrestia
Claims
What is claimed is:
1. A method for reducing leakage currents in a protective conductor
(PE) of an electricity network comprising a neutral conductor (N)
and a phase conductor (Lx) in addition to the protective conductor
(PE), the method comprising: determining a differential current
depending on a phase conductor current in the phase conductor (Lx)
and a neutral conductor current in the neutral conductor (N);
determining a frequency spectrum of the determined differential
current; generating the compensation current based on the
determined frequency spectrum and a predefined phase shift; and
feeding the compensation current into the phase conductor (Lx)
and/or into the neutral conductor (N), said compensation current
compensating for a leakage current caused by the differential
current.
2. The method as claimed in claim 1, wherein the differential
current is determined by a differential current converter.
3. The method as claimed in claim 1, further comprising converting
the determined differential current into a digital differential
current using an analog-to-digital converter.
4. The method as claimed in claim 1, further comprising generating
the compensation current depending on the determined differential
current and a predefined phase shift.
5. The method as claimed in claim 1, further comprising feeding in
the compensation current via a capacitive coupling.
6. The method as claimed in claim 1, further comprising feeding in
the compensation current via an inductive coupling.
7. The method as claimed in claim 1, further comprising feeding in
the compensation current via a galvanic coupling.
8. The method as claimed in claim 1, wherein the compensation
current is generated to have a frequency spectrum based on the
determined a frequency spectrum of the determined differential
current.
9. A device for reducing leakage currents in a protective conductor
(PE) of an electricity network comprising a neutral conductor (N)
and a phase conductor (Lx) in addition to the protective conductor
(PE), the device comprising: a determining unit for: determining a
differential current depending on a phase conductor current in the
phase conductor (Lx) and a neutral conductor current in the neutral
conductor (N), determining a frequency spectrum of the determined
differential current, and generating the compensation current based
on the determined frequency spectrum and a predefined phase shift;
and an infeed unit for feeding a compensation current into the
phase conductor (Lx) and/or into the neutral conductor (N), said
compensation current compensating for a leakage current caused by
the differential current.
10. A charging device for charging an electrical energy storage
element with the electricity network and the device as claimed in
claim 9.
11. The charging device as claimed in claim 10, wherein the
charging device is a galvanically non-isolated charging device.
12. The device as claimed in claim 9, wherein the determining unit
generates the compensation current to have a frequency spectrum
based on the determined a frequency spectrum of the determined
differential current.
Description
CROSS-REFERENCE TO RELATED APPLICATION
This application claims priority to German Patent Application No.
DE 10 2018 118 259.7, filed Jul. 27, 2018, which is incorporated by
reference herein in its entirety.
FIELD OF THE INVENTION
The invention relates to a method for reducing leakage currents in
a protective conductor of an electricity network comprising a
neutral conductor and a phase conductor in addition to the
protective conductor. Further subject matter of the invention is a
device for carrying out such a method.
BACKGROUND OF THE INVENTION
Particularly in electricity networks to which power converters are
connected without galvanic isolation, i.e. without an isolation
transformer, leakage currents caused by the power converter can
occur in the protective conductor of the electricity network. If
the leakage current exceeds a predefined value, this generally has
the effect that a residual current device (RCD) trips and
interrupts the current flow. In this case, the residual current
device cannot differentiate between such operation-dictated leakage
currents, i.e. leakage currents caused for example by a power
converter, and leakage currents caused by an isolation fault.
Undesired shutdowns that restrict the availability of the
electricity network or the power converter therefore occur.
US 2014 210 411 A1, which is incorporated by reference herein,
discloses a method for reducing leakage currents in a protective
conductor of an electricity network, wherein, by means of a passive
compensation circuit, a compensation current is generated and is
introduced into the protective conductor in order to compensate for
leakage currents. The compensation circuit comprises a transformer,
a diode rectifier and a voltage divider and is galvanically
connected to the protective conductor. In the case of this method,
it has proved to be disadvantageous that the corresponding
compensation circuit occupies a relatively large structural space
and has a high weight, with the result that it fails to be
sufficiently suitable for application onboard a vehicle.
Against this background, the problem addressed is that of reducing
undesired leakage currents in an electricity network having a
neutral conductor with a compact compensation circuit having a
lower weight.
SUMMARY OF THE INVENTION
What is proposed for solving the problem is a method for reducing
leakage currents in a protective conductor of an electricity
network comprising a neutral conductor and a phase conductor in
addition to the protective conductor, wherein a differential
current is determined depending on a phase conductor current in the
phase conductor and a neutral conductor current in the neutral
conductor and a compensation current is fed into the phase
conductor and/or into the neutral conductor, said compensation
current compensating for a leakage current caused by the
differential current.
In the method according to aspects of the invention, the leakage
current in the protective conductor is not measured directly, but
rather ascertained indirectly by a differential current that
corresponds to the leakage current being determined. Said
differential current is determined as a difference between the
currents in the phase conductor and the neutral conductor.
Depending on the differential current determined, a compensation
current is generated and fed into the phase conductor and/or into
the neutral conductor.
The measurement and the compensation of the leakage current can
thus be carried out without galvanic connection to the protective
conductor, for which reason a galvanic isolation in the
corresponding compensation circuit, for example by means of a
transformer, is not required. As a result, the compensation circuit
can be embodied compactly and with low weight.
In accordance with one advantageous configuration of the invention,
the differential current is determined by means of a differential
current converter. The differential current converter can comprise
a measurement pick-up, in particular in the manner of a clip-on
ammeter, which encloses the phase conductor and the neutral
conductor. A galvanic connection is not necessary, and so the
differential current can be determined in a non-contact manner. The
differential current resulting from the vectorial sum of the
currents flowing in the phase conductor and the neutral conductor
and having different current directions is preferably determined by
means of the differential current converter. In the case of such a
measurement by means of a differential current converter, the
protective conductor is not led through the differential current
converter.
One advantageous configuration provides for the differential
current determined to be converted into a digital differential
current by means of an analog-to-digital converter. The provision
of a digital differential current makes possible the digital
processing of the differential current determined, for example in a
microcontroller or a digital filter. In this way, the structural
space required for the compensation circuit can be further reduced
and the susceptibility of the compensation circuit to interference
can be reduced.
In accordance with one advantageous configuration of the invention,
the compensation current is generated depending on the differential
current determined and a predefined phase shift. Particularly
preferably, the magnitude of the compensation current is identical
to the magnitude of the differential current. The predefined phase
shift is preferably 180.degree..
It is preferred if a frequency spectrum of the differential current
determined is determined. Determining the frequency spectrum makes
it possible to identify dominant spectral components in the
differential current and to generate the compensation current in
accordance with said spectral components. It has proved to be
particularly advantageous if the frequency spectrum of the
differential current determined is determined in a frequency range
of 20 Hz to 300 kHz. A Fourier transformation, in particular a fast
Fourier transformation (FFT), can be used for determining the
frequency spectrum. Alternatively, the frequency spectrum can be
ascertained by means of a p-Burg algorithm or a trigonometrical
algorithm.
In this context, it has proved to be advantageous if the
compensation current is generated depending on the frequency
spectrum determined and a predefined phase shift. The predefined
phase shift is preferably 1800.
The compensation current can be output by means of a
digital-to-analog converter or by means of an amplifier, in
particular by means of a rail-to-rail (R2R) amplifier or a class D
amplifier.
Preferably, the compensation current is fed into the phase
conductor and/or the neutral conductor via a capacitive coupling,
with the result that a galvanic coupling to the protective
conductor is not required.
In accordance with an alternative, preferred configuration, the
compensation current is fed into the phase conductor and/or the
neutral conductor via an inductive coupling.
In accordance with a further, alternative preferred configuration,
the compensation current is fed into the phase conductor and/or the
neutral conductor via a galvanic coupling.
Furthermore, a contribution is made to solving the problem
mentioned in the introduction by a device for reducing leakage
currents in a protective conductor of an electricity network
comprising a neutral conductor and a phase conductor in addition to
the protective conductor, wherein the device comprises a
determining unit for determining a differential current depending
on a phase conductor current in the phase conductor and a neutral
conductor current in the neutral conductor and comprises an infeed
unit for feeding a compensation current into the phase conductor
and/or into the neutral conductor, said compensation current
compensating for a leakage current caused by the differential
current.
Further subject matter of the invention is a charging device for
charging an electrical energy storage element with an electricity
network and a device described above.
The same advantageous effects as have already been described in
association with the method according to aspects of the invention
can be achieved in the case of the device for reducing leakage
currents and the charging device.
In accordance with one advantageous configuration of the charging
device, provision is made for the latter to be configured as a
galvanically non-isolated charging device.
Alternatively or additionally, in the case of the device and/or the
charging device, the advantageous configurations and features
described in association with the method according to aspects of
the invention can also find application alone or in
combination.
BRIEF DESCRIPTION OF THE DRAWING
Further details and advantages of the invention will be explained
below on the basis of the exemplary embodiments shown in the
figures, in which:
FIG. 1 shows a device for reducing leakage currents in a protective
conductor of an electricity network in a schematic illustration;
and
FIG. 2 shows a flow diagram of one exemplary embodiment of a method
according to aspects of the invention for reducing leakage
currents.
DETAILED DESCRIPTION OF THE INVENTION
The illustration in FIG. 1 shows an electricity network 10 having a
phase conductor LX, a neutral conductor N and a protective
conductor PE. Said electricity network 10 can be a supply network,
for example, which is connected to a charging device for charging
an electrical energy storage element of a vehicle, in particular of
an electric or hybrid vehicle. The charging device is preferably a
galvanically non-isolated charging device. The electricity network
10 is connected to a device 1 for reducing leakage currents in the
protective conductor PE, which device will be explained in detail
below:
The device 1 comprises a determining unit for determining a
differential current, said determining unit being embodied as a
differential current converter 2 and monitoring, in particular
continuously, the phase conductor Lx and the neutral conductor N.
In this respect, the phase conductor current in the phase conductor
Lx and the neutral conductor current in the neutral conductor N are
measured and the difference between these two currents is formed.
The differential current determined in this way corresponds to the
leakage current in the protective conductor PE. Therefore, it is
not necessary to monitor the protective conductor PE directly with
an ammeter.
A further component of the device 1 is an analog-to-digital
converter 3, which is connected to the differential current
converter 2. By means of the analog-to-digital converter 3, the
analog differential current is converted into a digital
differential current. The analog-to-digital converter 3 is
connected to a computing unit 4, which can be embodied as a
microcontroller, for example. A frequency spectrum of the
differential current can be determined by means of the computing
unit 4. By way of example, a fast Fourier transformation can be
carried out for this purpose. Optionally, as an alternative or in
addition, an analysis device 5 can be provided, which is connected
to the analog-to-digital converter 3. The analysis device 5 can be
configured to generate a frequency spectrum of the differential
current. If such an analysis device 5 is provided, it is not
necessary to carry out calculations for generating the frequency
spectrum in the computing unit 4. It is thereby possible to relieve
the burden on the computing unit 4.
Preferably, the frequency spectrum is determined in a range of 20
Hz to 300 kHz. The frequency spectrum contains amplitudes of the
respective frequencies.
On the basis of the frequency spectrum and also a predefined phase
shift, here 180.degree., the computing unit 4 generates an
unamplified compensation current signal, which is fed to an
amplifier 6 of the device 1. The amplifier 6 is preferably embodied
as a rail-to-rail amplifier or as a class D amplifier. A
digital-to-analog converter can alternatively be used instead of an
amplifier 6. The amplifier 6 or the digital-to-analog converter
generates a compensation current, which is fed to a switching
device 7. By means of the switching device 7, the compensation
current is selectively coupled to the phase conductor LX and/or the
neutral conductor N.
The compensation current is fed into the phase conductor and/or the
neutral conductor via a capacitive or an inductive infeed unit 11,
such that a galvanic coupling to the protective conductor is not
required. Alternatively, the infeed into the phase conductor and/or
the neutral conductor can be carried out by means of a galvanically
linked infeed unit.
Preferably, the computing unit 4 is configured to differentiate
operation-dictated leakage currents, such as may be caused for
example by a charging device that is not galvanically isolated from
the electricity network 10, from undesired fault currents in the
protective conductor PE. By way of example, provision can be made
for the computing unit 4 to determine and store a characteristic
frequency spectrum generated as a result of operation-dictated
leakage currents. The computing unit is preferably configured to
compare a frequency spectrum determined during the continuous
monitoring of the differential current with the stored,
characteristic frequency spectrum. If the deviation of the
determined frequency spectrum from the stored, characteristic
frequency spectrum exceeds a predefined threshold value, it is
possible to generate a switching signal for driving the switching
device 7. An exceedance of said threshold value indicates an
undesired fault current. In such a case, the switching device 7 is
driven by the switching signal in such a way that a compensation
current is not fed into the phase conductor Lx and/or the neutral
conductor N. This has the consequence that the leakage current in
the protective conductor PE is not compensated for and a residual
current device (not illustrated in the drawing) can be activated by
the fault current in order to switch off the electricity network
10.
Further components of the device 1 are a diagnosis device 8 for
acquiring statistical data, which can be read out via a diagnosis
interface, and a programming device 9, via which the computing unit
4 can be programmed. By means of the programming device 9 it is
possible, for example, to set operating parameters of the computing
unit 4.
Furthermore, a self-calibration is implemented in the computing
unit 4, and is carried out upon the computing unit 4 being
started.
A method sequence 100 upon the computing unit 4 being started will
be explained in greater detail below with reference to the flow
diagram shown in FIG. 2. In an activation step 101, the device 1 is
switched on. In a self-test step 102 succeeding activation step
101, a self-test of the device 1 is started. In a step 103, the
functionality of the differential current converter 2 is checked.
In a step 104, the functionality of the analog-to-digital converter
3 is checked. In step 105, the functionality of the computing unit
4 is checked and, in step 106, the functionality of the amplifier 6
is checked. In a step 107, the functionality of a watchdog of the
computing unit 4 is tested. In step 108, a test of the diagnosis
device 8 is carried out and, in step 109, a test of a
self-calibration procedure is carried out.
If all of the checks are concluded positively, the device is
transferred to an operating state in step 110. In the operating
state 110, the differential current is determined depending on the
phase conductor current in the phase conductor Lx and the neutral
conductor current in the neutral conductor N and a compensation
current is fed into the phase conductor Lx and/or into the neutral
conductor N, said compensation current compensating for a leakage
current caused by the differential current.
LIST OF REFERENCE SIGNS
1 Device for reducing leakage currents 2 Differential current
converter 3 Analog-to-digital converter 4 Computing unit 5 Analysis
unit 6 Amplifier 7 Switching device 8 Diagnosis device 9
Programming device 10 Electricity network 11 Infeed unit 100 Method
sequence 102-109 Test steps 110 Operating state Lx Phase conductor
N Neutral conductor PE Protective conductor
* * * * *